1. Field of the Invention
The present invention relates to a motor, and particularly, to a rotor of a motor and a manufacturing method thereof which can simplify assembly operation, reduce manufacturing time and allow firm coupling of a magnet.
2. Description of the Background Art
A motor is a device for converting electric energy into kinetic energy, and is used as a power source of almost every machine. The motor is classified into a DC motor, a BLDC motor (Brush Less Direct Current Motor), an induction motor, a synchronous motor, a universal motor or the like.
In general, the BLDC motor includes a stator in which a coil winds around a laminated core, a rotor having a magnet and rotatably inserted into a through hole formed inside the stator, and a hole sensor for sensing a pole of the rotor magnet.
In the BLDC motor, the rotor is rotated by the interaction between a magnetic field generated by an electric current applied to the wound coil and a magnetic field generated by the magnet of the rotor. The hole sensor senses the pole of the magnet and controls the electric current supplied to the coil.
FIG. 1 is a sectional view illustrating a rotor of an SPM (Surface Permanent Magnet) type BLDC motor. FIG. 2 is a side view of the rotor. As illustrated therein, the rotor of the BLDC motor includes a cylindrical rotor core 100 in which a plurality of disc-shaped sheets 110 having uniform thickness are laminated to have a certain length and an outer diameter, and a plurality of curved plate-shaped magnets 200 having a certain thickness and attached to an outer circumferential surface of the rotor core 100. The disc-shaped sheet 110 is formed of silicon steel. The disc-shaped sheets 110 laminated in a cylindrical shape are fixedly coupled with each other by a welding or bolting.
There are four curved plate-shaped magnets 200. A radius of curvature of the magnet 200 corresponds to that of the rotor core 100. When the four curved plate-shaped magnets 200 are attached to the outer circumferential surface of the rotor core 100, the four curved plate-shaped magnets form a cylindrical shape. That is, the four curved plate-shaped magnets 200 completely cover the outer circumferential surface of the rotor core 100.
The curved plate-shaped magnets 200 are attached to the outer circumferential surface of the rotor core 100 by an adhesive 210. A shaft hole 120 is penetratingly formed at the center of the rotor core 100. Parts 300 and 400 indicated by a virtual line are a stator and a motor shaft, respectively.
A method for manufacturing the rotor of the BLDC motor is as follows. First, as illustrated in FIG. 3, a plurality of disc-shaped sheets 110 are manufactured by a press process and are laminated to form a cylindrical shape. The disc-shaped sheets 110 are fixedly coupled with each other by bolting or welding, and so on, thereby manufacturing the rotor core 100.
After the adhesive 210 is applied to the outer circumferential surface of the rotor core 100, the curved plate-shaped magnets 200 are attached to the outer circumferential surface of the rotor core 100. Then, the adhesive 210 is dried.
The magnets 200 are attached to the outer circumferential surface of the rotor core 100 after the curved plate-shaped magnets 200 are magnetized. The curved plate-shaped magnets 200 may be attached to the rotor core 100 and then magnetized.
However, since in the rotor of the conventional BLDC motor, several curved plate-shaped magnets 200 are adhered and fixed to the outer circumferential surface by using the adhesive 210, a series of adhering processes to adhere the curved plate-shaped magnets 200 and a process of drying the adhesive 210 are required, thereby increasing the manufacturing time. Accordingly, assembly productivity of the rotor of the motor is significantly deteriorated.
In addition, since the curved plate-shaped magnets 200 are attached to the outer circumferential surface of the rotor core 100 by the adhesive 210, the defective adhering of curved plate-shaped magnets 200 is more likely to occur. In this case, the curved plate-shaped magnets 200 are apart from the rotor core 100 to cause the damage to the motor during the operation of the motor.
In addition, the rotor is inserted into the through hole of the stator. The narrower an interval between the outer circumferential surface of the rotor and an inner circumferential surface of the through hole is, the higher the motor efficiency is. However, the curved plate-shaped magnets 200 are attached to the outer circumferential surface of the rotor core 100. If there is a large amount of the adhesive 210, the adhesive 210 protrudes from between the curved plate-shaped magnets 200 and is hardened. Thus, the hardened adhesive 210 comes in contact with an inner wall of the through hole of the stator during the operation of the motor to thereby increase rotary resistance of the rotor.